Various dipeptide derivatives described in WO 2004/048400 show antiarrhythmic activity which is comparable to the antiarrhythmic activity of an antiarrhythmic peptide, such as an AAP, AAP10, HP5 peptide compound or functional analogue thereof. Said dipeptide compounds have been shown to increase the time to an AV block in a mouse after infusion of CaCl2, in what is referred to herein as a “standard calcium-induced arrhythmia assay.” This increase in time has been shown to be substantially the same as for AAP, i.e., these prior art compounds show time lags of approximately the same duration. However, AAP, as well as certain AAP derivatives, are thought to have some undesired features, e.g., low stability and a need for high doses before therapeutic efficacy is achieved. Moreover, the compounds of WO 2004/048400 have been shown to inhibit the activity of isozyme 3A4 of cytochrome P 450 oxidase, which is an important drug metabolising enzyme in mammals. As these compounds are often administered to patients in combination with other drugs, inhibition of the P450 oxidase by the antiarrhythmic has the potentially undesirable effect of altering the physiological effect of the other drugs.